root [ 1 ] TH1F * h=new TH1F ("h","example histogram",100,0.,5.);
root [ 2 ] ifstream inp; double x;
root [ 3 ] inp.open("expo.dat") ;
root [ 4 ] while (!(inp >> x)==0){h->Fill(x);}
root [ 5 ] h->Draw( );
root [ 6 ] inp.close( ) ;